1. Field of the Invention
The present invention relates to improvements of a controller of an alternating current (AC) type plasma display panel (PDP) having a memory function and a method of write/erasing thereof.
2. Description of the Related Art
A tendency to use a plane type display unit such as a liquid crystal display and a PDP having a small depth in place of a deep cold cathode ray tube (CRT) has been developed in recent years by the requirement of forming electronic equipment compact in size. For example, an AC type PDP is developed, and improvement of resolution and display quality are aimed at. The AC type PDP has a structure in which display cells each having a memory function are assembled.
According to the AC type PDP, a write address method is adopted in which a wide erasing pulse or a narrow erasing pulse is applied to a sustain electrode to complete a write operation in order to leave wall electric charges acting effectively on the address discharge of the AC type PDP. Address discharge is performed thereafter. When there is dispersion in the discharge starting voltage in each display cell, however, it is impossible to perform an erasing operation accurately, and the display quality is deteriorated.
Here, the related art of the present invention will be described according to FIGS. 1 through 5B. For example, a controller for controlling a PDP 25 of a three-electrode surface discharge type is provided with an X driver 1, a Y scan driver 2, a Y driver 3, an address driver 4 and a control circuit 5 as shown in FIG. 1. Besides, the PDP 25 has N lines.times.M rows.times.3 (R,G,B) pieces of display cells Cs each having a memory function.
The display cell Cs of one bit is provided with sustain electrodes (hereinafter referred to simply as an X electrode and a Y electrode) 6 and 7 (see FIG. 2) provided in the same plane, an address electrode 8 provided at a position opposing thereto, a protective film 9 for protecting the X electrode 6 and the Y electrode 7, and a phosphor 10 for coating the address electrode 8 and displaying in color.
As to the function of the controller concerned, a predetermined voltage Vx is supplied to the X electrode 6 from the X driver 1, and predetermined voltage Vy is supplied to the Y driver 3. With this, the Y electrode 7 is scanned by the Y scan driver 2, and the predetermined voltage Vy is supplied to the Y electrode 7. On the other hand, when address data are supplied to the address driver 4 from the control circuit 5, the display cell Cs is selected and luminance display is made.
Namely, in the PDP 25, a predetermined voltage waveform (hereinafter referred to as a sustain pulse) is applied alternately to two pieces of X and Y electrodes 6 and 7, thereby to sustain discharge and make a luminance display. Here, discharge is terminated within 1 .mu.s to several .mu.s immediately after the pulse is applied. Further, negative voltage is applied to positive electric charges (ions) generated by the discharge and which are accumulated on the surface of the protective film (insulating layer) 9 on the X electrode 6, for instance, where negative voltage is applied. Similarly, negative electric charges (electrons) are accumulated on the surface of the phosphor 10 (insulating layer) on the Y electrode 7 applied with positive voltage.
Therefore, discharge is generated between the electrodes 6 and 7 by supplying a write voltage (hereinafter referred to also as a write pulse) having a high voltage value at the beginning between the X and Y electrodes 6 and 7, thus forming wall electric charges. Thereafter, when a sustain voltage having a different polarity is applied between the X and Y electrodes 6 and 7 at a lower value than the last occasion, the wall electric charges accumulated previously are overlapped onto the sustain voltage.
With this, the relative voltage to the discharge space of the display cell Cs becomes higher and exceeds a discharge threshold value and the display cell Cs starts to discharge. In other words, the display cell Cs, in which write discharge is carried out first and the wall electric charges are generated, has such a feature that discharge is sustained by applying a sustain pulse of a reverse polarity alternately thereafter.
In general, such a state is called a memory effect or a memory function, and display is made by utilizing such a memory effect in the AC type PDP 25.